Testing: Improve "Testcontainers for Python" implementation about cratedb-toolkit

[amotl]

Together with @pilosus, we have been able to bring in a few advancements to the "Testcontainers for Python" adapter implementations we are running here. Thanks!

• #78
• Testing: Add Testcontainer for MongoDB with improved configurability
• #82

[amotl]

It will be nice to have a modern test layer which forms a cluster, for both Java and Python.

If we would like to contribute the existing implementation early, I think it makes sense to think about another detail of "naming things" on this matter.

If we would like to have CrateDBContainer to be the one and only to be responsible to spin up single-node instances, while there will be future implementations permitting to run whole clusters, I think it can make sense to reflect that into a naming scheme like CrateDBSingleNodeContainer vs. CrateDBMultiNodeContainer.

However, while writing that down, it could also be a dual-class machinery of the existing CrateDBContainer and an additional CrateDBClusterManager, which, well, manages the former.

It is probably too early to think about this topic without getting hands-on with it, mainly starting by researching how others might be doing similar things like managing a fleet of containers on behalf of a single convenience entrypoint.